In the manufacture of plastic materials such as bar soaps, the soap is generally extruded from a nozzle to form a continuous soap plug. Thereafter the plug is cut into smaller pieces called soap billets, whereupon the billet is then stamped to form individual bars of soap. Typical methods of stamping the billets into individual bars of soap involve the use of soap stamping machines. Exemplary machines which have been readily available in the marketplace include: the 1984 "Type AT-A" manufactured by G. Mazzoni: S.P.A. Busto Arsizo--Italy; and the 1985 "USN O" manufactured by Binacchi & Co., Via Gromsci 21045, Gazzada Schianno (Varese) Italy. Such machines have a pair of dies with their peripheral surfaces or lands adapted to meet in substantial face-to-face contact thereby compressing the billet between the pair of dies to give the bar its desired shape and final appearance. The stamping of billets between the forming dies gives each bar a uniform shape and a smooth and glossy surface. It also typically imprints a design such as a logo or trademark onto an area of the surface of the bar.
With the development of milder synthetic based formulas for soap bars, soap billets have become stickier and tend to press poorly within the dies, resulting in the individual bars having a poor final appearance. The problem has been that the milder soap formula tends to stick to the die during stamping. The soap material that sticks to the die makes an imprint on the next billet that is stamped, resulting in subsequent soap bars having an unsightly appearance. Because of this, production lines must be shut down in order to frequently clean the dies. This is inefficient and increases manufacturing costs, which ultimately increases the price of the final product to the consumer. Various methods have been used in the past to circumvent the aforementioned problem but none of them have solved the problem satisfactorily.
One method used in the past to prevent soap from sticking to the dies was to chill the dies on the production line. Soap plugs are usually at an elevated temperature when entering the stamping apparatus so that the billet can be easily molded into the desired shape. The difference in temperatures between the chilled dies and the soap billets reduces the amount of material sticking to the die during the stamping process. However, because the dies are chilled, water tends to condense on the dies and eventually forms frost. Frost sticking to the die tends to form an unsightly imprint on the soap bars in the same way that soap material sticking to the die does. Furthermore, the cold die cools the soap billet which reduces its malleability and causes the soap to shape poorly within the dies.
Another method used in the past was to place die liquors on the dies. Substances such as Brine or Alcohol when placed on the dies tend to reduce the amount of material sticking to the die during the stamping process. However, this method has many drawbacks. Some of the liquors that are used tend to interfere with and change the soap's chemical formulation and adversely affect the perfumes that are present in the soaps. Furthermore, if the dies are made of brass, as is common, some of the die liquors tend to corrode the dies. Lastly, the use of die liquors is very messy when used on line and is expensive, ultimately resulting in an increase in the price of the final product.
It is therefore an object of the present invention to provide an improvement to a method and apparatus for stamping blanks of plastic material into shaped articles, wherein plastic material is substantially prevented from sticking to the dies.
It is another object of the present invention to apply such improvements to the manufacture of soap bars.
It is another object of the present invention to provide such an improvement that is inexpensive and can readily be adapted to accommodate existing soap stamping methods and apparatus.
The aforementioned and other objects of the invention will become more apparent hereinafter.